A book I'm reading about Elizabethan poets tells me that "lapis" is an adjective meaning "insensate" or "lacking empathy". I had to question that in my mind since I've always associated the word with a jewelled stone, as in "lapis lazuli". Looking up an online dictionary, I find that to be correct. "Lapis" means stone, and is a noun, not an adjective. But maybe there is a secondary meaning which isn't listed. Can anyone throw any light on this?

Generally, can Latin nouns be converted into adjectives? In English many of our adjectives are derived from a noun, so, for example, we can turn "stone" into an adjective "stony". Can you do the same in Latin?

In English you say "stone" as well as "stony" ("a stone wall" before "a stoney wall"). Many would use the latin word "lapis" for "stone" in English and use it also an an adjective. But that is in English only.

Lapis cannot itself be used as an adjective, unless you think of a noun's genitive as adjectival, which in a sense it is.

One common way of making nouns into adjectives, when talking about the material of which something is made, is with the addition of -eus -ea -eum. So, lāneus means 'woolen' (from lāna, 'wool'), ferreus means 'of iron' (from ferrum, 'iron'), ligneus means 'wooden' (from lignum, 'wood'), and similarly aureus, argenteus, and, indeed, lapideus. Another way is to add -ōsus -ōsa -ōsum to the noun's stem, equivalent to '-ful' in English. So, formōsus means 'beautiful' (from forma, 'beauty, form'), cūriōsus means 'careful' (from cūra, 'care') and so on. Lapidōsus means 'stony' or 'full of stone'.

Both lapideus and lapidōsus could, I think, be understood as meaning 'hard-hearted' or 'unfeeling', though the usual word for this in Latin is dūrus.

Those are the two ways of adjectifying a noun that are relevant to your question, but there are other ways. For instance, the addition of -fer -fera -ferum (or -ger -gera -gerum) makes an adjective meaning '____-carrying'. Lucifer means 'light-bearing' or 'radiant one', mare navigerum means 'ship-carrying' or 'navigable sea', Aeneas penātifer is 'Penates-carrying Aeneas', and, to coin a word, servi lapidiferi would be 'stone-carrying slaves'.

Craig_Thomas wrote:Lapis cannot itself be used as an adjective, unless you think of a noun's genitive as adjectival, which in a sense it is.

One common way of making nouns into adjectives, when talking about the material of which something is made, is with the addition of -eus -ea -eum. So, lāneus means 'woolen' (from lāna, 'wool'), ferreus means 'of iron' (from ferrum, 'iron'), ligneus means 'wooden' (from lignum, 'wood'), and similarly aureus, argenteus, and, indeed, lapideus. Another way is to add -ōsus -ōsa -ōsum to the noun's stem, equivalent to '-ful' in English. So, formōsus means 'beautiful' (from forma, 'beauty, form'), cūriōsus means 'careful' (from cūra, 'care') and so on. Lapidōsus means 'stony' or 'full of stone'.

Both lapideus and lapidōsus could, I think, be understood as meaning 'hard-hearted' or 'unfeeling', though the usual word for this in Latin is dūrus.

Those are the two ways of adjectifying a noun that are relevant to your question, but there are other ways. For instance, the addition of -fer -fera -ferum (or -ger -gera -gerum) makes an adjective meaning '____-carrying'. Lucifer means 'light-bearing' or 'radiant one', mare navigerum means 'ship-carrying' or 'navigable sea', Aeneas penātifer is 'Penates-carrying Aeneas', and, to coin a word, servi lapidiferi would be 'stone-carrying slaves'.

Thanks for the detailed reply. That seems to clear it up. Concerning the noun, I was thinking there were probably two different words to describe what in English we have one word for: to us, "stone" can mean precious stone (gem), or it can just mean building stone. I speculated that the Romans had two disctinctive words, with "lapis" restricted to gemstones. But I've just looked at the English and Latin texts of Caesar's Gallic commentaries, and I see he does use "lapis" and "lapidibus" when talking of stone of the non-precious kind.